Catalyst component comprising a metallocene with two tetrahydroindenyl ligands for producing a polyolefin

ABSTRACT

Provided is a catalyst component for producing a polyolefin, which catalyst component comprises a metallocene catalyst having a structure according to formula (I): (THI) 2 R″MQ p , wherein each THI is a tetrahydroindenyl derivative which may be substituted or unsubstituted, provided that at least one of the tetrahydroindenyl derivatives is substituted at the 2-position or the 4-position; R″ is a structural bridge to impart stereorigidity between the two THI groups; M is a metal from Group IIIB, IVB, VB or VIB; Q is a hydrocarbyl group having from 1-20 carbon atoms, or a halogen; and p is the valence of M minus 2.

The present invention relates to a catalyst component and catalystsystem for use in preparing polyolefins, especially polyethylene havinga high molecular weight and improved mechanical properties, whilstretaining good processing properties. The invention further relates to aprocess for producing polyolefins using the catalyst component orcatalyst system.

Metallocene catalysts have been known to be useful in the production ofpolyolefins for some time. The first generation of metallocene catalystswere unbridged metallocenes. These catalysts provided a new route intopolyolefin resins. However, polyolefin resins produced using unbridgedmetallocenes were found to have poor processibility, despite having goodoptical properties, such as high transparency and low haze.

In order to improve the properties of the resins, bridged metallocenecatalysts were developed. Such bridged metallocene catalysts aredisclosed in published PCT application number WO91/03500. Typical suchsupported bridged metallocenes are Et(IndH₄)₂ZrCl₂ and Et(Ind)₂ZrCl₂(IndH₄ is an unsubstituted tetrahydroindenyl (THI) group, and Ind is anunsubstituted indenyl group). Other such known bridged metallocenescomprise substituted cyclopentadienyl ligands, such as those disclosedin published patent U.S. Pat. No. 4,892,851. In these metallocenes, thesubstitution pattern was designed with a view to controlling thestereochemistry of polypropylene produced from the catalysts.

Resins produced from this second generation of metallocene catalystsdisplay improved mechanical properties due to their higher molecularweight. In addition, such resins have better processing properties dueto the presence of different chain architecture and probably long chainbranches. However, the processibility and the co-monomer content of suchresins is still less than is desired.

Resins produced from Ziegler-Natta and chromium-based catalysts may havethe same or similar processing and mechanical properties as comparedwith their counterparts formed using metallocene catalysts. However,such resins display inferior optical and mechanical properties.

Thus, it is still desirable to produce high quality resins usingmetallocene catalysts that have more superior mechanical and processingproperties.

It is an object of the present invention to overcome the problemsassociated with the above prior art catalysts. Accordingly, the presentinvention provides a catalyst component for producing a polyolefin,which catalyst component comprises a metallocene catalyst having astructure according to a formulae (I):(THI)₂R″MQ_(p)  (I)wherein each THI is a tetrahydroindenyl derivative which may besubstituted or unsubstituted, provided that at least one of thetetrahydroindenyl derivatives is substituted at the 2-position and/orthe 4-position; R″ is a structural bridge to impart stereorigiditybetween the two THI groups; M is a metal from Group IIIB, IVB, VB orVIB; Q is a hydrocarbyl group having from 1-20 carbon atoms, or ahalogen; and p is the valence of M minus 2. Preferably, the substituentat the 4-position is bulky, and more preferably, it is cyclic.

By substituted, in the context of the present invention it is meant thatany of the positions on the tetrahydroindenyl group may comprise asubstituent in place of a hydrogen atom. Thus, whilst each substitutedTHI group may be a tetrahydroindenyl group with the substituent presenton the five-membered ring, it may alternatively be a group thatcomprises the same pattern of saturation as tetrahydroindenyl, but inwhich one or more of the hydrogen atoms on the six-membered ring hasbeen replaced. Alternatively, and preferably, the substituents may bepresent on both the five-membered and the six-membered ring.

Each catalyst component comprises two THI derivative ligands. The twoligands may be different. However, it is preferred that the two THIligands of the catalyst component are the same.

The present invention further provides a method for producing apolyolefin, which method comprises polymerising an olefin monomer (or anolefin monomer and a co-monomer) in the presence of a catalyst component(or catalyst system comprising the catalyst component) as defined above.

The substitution pattern of the THI ligands on the metallocene catalystsleads to the advantages of the present invention. The substitutionpattern and numbering of the ligands of the present catalysts will bediscussed in more detail below.

The ligand, THI, used in catalysts of formula (I) is atetrahydroindenyl-type ligand, in which, in the context of the presentinvention, the substituent positions are numbered from 1-7 according tothe system set out in the structure below:

To distinguish substitution in the first THI ligand from the second, thesecond is numbered according to the same system, but from 1′-7′, inaccordance with convention. In this type of catalyst, the position ofthe bridge is not particularly limited, and is preferably a 1,1′-bridge,a 2,2′-bridge or a 1,2′-bridge, a 1,1′-bridge being most preferred.

The position of the substituent or substituents on the two THI ligandsis not particularly limited, provided that at least one of the ligandsis substituted in the 2-position and/or the 4-position. Provided thatthis criterion is satisfied, the THI ligands may have any substitutionpattern, including being unsubstituted or fully substituted. Inpreferred embodiments both of the THI ligands are substituted.Typically, both of the THI ligands comprise substituents in the2-position and/or in the 4-position. Most preferably both of the THIligands comprise substituents in the 2-position and the 4-position. Inthese embodiments the other positions in the ring may also comprisesubstituents, or may be unsubstituted. Particularly preferredmetallocene catalysts with a 1,1′-bridge have the following substitutionpatterns: 2; 4; 2,4; 2,2′; 4,4′; 2,4′; 2,4,2′; 2,4,4′; and 2,4,2′,4′wherein only those positions indicated comprise a substituent. It shouldbe noted that since the basic structures of both THI derivatives areidentical, patterns such as 2,4′ and 4,2′ are identical.

The use of a catalyst as defined above (in which the THI derivatives aresubstituted according to the above specific substitution patterns) toproduce a polyolefin, leads to polyolefins that have improved physicaland mechanical properties, are easily processed and have good opticalproperties.

Thus, the polyolefin resins produced by the catalyst system of thepresent invention have improved processibility and solidificationproperties in injection blow moulding and injection moulding, whilstsimultaneously showing high transparency and flexibility.

The substituent or substituents present on the THI ligands in theabove-described catalysts are not particularly limited. The aboveligands, when comprising more than one substituent, may be substitutedwith the same substituent throughout, or with different substituents.Typically the substituents are independently selected from an aryl groupand a hydrocarbyl group having from 1-20 carbon atoms. They includephenyl (Ph), benzyl (Bz), naphthyl (Naph), indenyl (Ind) and benzindenyl(BzInd), as well as Me, Et, n-Pr, i-Pr, n-Bu, t-Bu, Me₃Si, alkoxy(preferably R—O, where R is C₁-C₂₀ alkyl), cycloalkyl, and halogen. Themost preferred substituents at the 2-position are methyl groups. Themost preferred substituents at the 4-position are phenyl, naphtyl andbenzindenyl.

Preferred THI derivatives include: 2-Me,4-PhTHI; 2-Me,4-NaphTHI; and2-Me,4,5-BzIndTHI. The most preferred catalyst components comprise atleast one on these ligands, and preferably two such ligands. It isparticularly preferred that the two THI ligands of the catalystcomponents are the same.

The type of bridge present between the THI rings in the present catalystcomponents is not itself particularly limited. Typically R″ comprises analkylidene group having 1 to 20 carbon atoms, a germanium group (e.g. adialkyl germanium group), a silicon group (e.g. a dialkyl silicongroup), a siloxane group (e.g. a dialkyl siloxane group), an alkylphosphine group or an amine group. Preferably, the substituent comprisesa hydrocarbyl radical having at least one carbon atom to form thebridge, such as a substituted or unsubstituted ethylenyl radical (e.g.Et, —CH₂CH₂—). Most preferably R″ is Et or Me₂Si.

The metal, M, in the metallocene catalyst is preferably a metal fromGroup IIIB, IVB, VB or VIB of the periodic table. Typically, M is Ti,Zr, Hf, or V and Q is preferably a halogen, typically Cl. Typically thevalence of the metal is 4, such that p is 2.

The most preferred catalyst components of the present invention are:

-   Me₂Si(2-MeTHI)₂ZrCl₂-   Et(2-MeTHI)₂ZrCl₂-   Me₂Si(2-Me,4-PhTHI)₂ZrCl₂-   Et(2-Me,4-PhTHI)₂ZrCl₂-   Me₂Si(2-Me,4-NaphTHI)₂ZrCl₂-   Et(2-Me,4-NaphTHI)₂ZrCl₂-   Me₂Si(2-Me,4,5-BzIndTHI)₂ZrCl₂-   Et(2-Me,4,5-BzIndTHI)₂ZrCl₂

The catalyst system of the present invention is not particularly limitedprovided that it comprises at least one metallocene catalyst componentas defined above. Thus the system may comprise further catalysts, ifnecessary, such as further metallocene catalysts according to thepresent invention, or other catalysts.

The catalyst system of the present invention comprises, in addition tothe above catalyst component, one or more co-catalysts capable ofactivating the metallocene catalyst. Typically, the co-catalystcomprises an aluminium- or boron-containing co-catalyst.

Suitable aluminium-containing co-catalysts comprise an alumoxane, analkyl aluminium compound and/or a Lewis acid.

The alumoxanes that can be used in the present invention are well knownand preferably comprise oligomeric linear and/or cyclic alkyl alumoxanesrepresented by the formula (A):

-   for oligomeric linear alumoxanes; and formula (B)-   for oligomeric cyclic alumoxanes,    wherein n is 140, preferably 10-20; m is 3-40, preferably 3-20; and    R is a C₁-C₈ alkyl group, preferably methyl. Generally, in the    preparation of alumoxanes from, for example, aluminium trimethyl and    water, a mixture of linear and cyclic compounds is obtained.

Suitable boron-containing co-catalysts may comprise a triphenylcarbeniumboronate, such as tetrakis-pentafluorophenyl-borato-triphenylcarbeniumas described in EP-A-0427696:

or those of the general formula below, as described in EP-A-0277004(page 6, line 30 to page 7, line 7):

The catalyst system may be employed in the gas phase or in a solutionpolymerisation process, which is homogeneous, or a slurry process, whichis heterogeneous in a single or tandem reactor configuration. In asolution process, typical solvents include hydrocarbons having 4-7carbon atoms such as heptane, toluene or cyclohexane. In a slurryprocess it is necessary to immobilise the catalyst system on an inertsupport, particularly a porous solid support such as talc, inorganicoxides and resinous support materials such as polyolefin. Preferably,the support material is an inorganic oxide in its finely divided form.

Suitable inorganic oxide materials which are desirably employed inaccordance with this invention include group IIA, IIIA, IVA, or IVBmetal oxides such as silica, alumina and mixtures thereof. Otherinorganic oxides that may be employed either alone or in combinationwith the silica, or alumina are magnesia, titania, zirconia, and thelike. Other suitable support materials, however, can be employed, forexample, finely divided functionalised polyolefins such as finelydivided polyethylene.

Preferably, the support is a silica support having a surface area offrom 100-1000 m²/g, more preferably from 200-700 m²/g, and a pore volumeof from 0.5-4 ml/g, more preferably from 0.5-3 ml/g.

The amount of alumoxane and metallocenes usefully employed in thepreparation of the solid support catalyst can vary over a wide range.Generally the aluminium to transition metal mole ratio is in the rangebetween 1:1 and 100:1, preferably in the range 5:1 and 80:1 and morepreferably in the range 5:1 and 50:1.

The order of addition of the catalyst and alumoxane to the supportmaterial can vary. In accordance with a preferred embodiment of thepresent invention alumoxane dissolved in a suitable inert hydrocarbonsolvent is added to the support material slurried in the same or othersuitable hydrocarbon liquid and thereafter the catalyst component isadded to the slurry.

Preferred solvents include mineral oils and the various hydrocarbonswhich are liquid at reaction temperature and which do not react with theindividual ingredients. Illustrative examples of the useful solventsinclude the alkanes such as pentane, iso-pentane, hexane, heptane,octane and nonane; cycloalkanes such as cyclopentane and cyclohexane,and aromatics such as benzene, toluene, ethylbenzene and diethylbenzene.

Preferably the support material is slurried in toluene and the catalystcomponent and alumoxane are dissolved in toluene prior to addition tothe support material.

The polyolefins that the present catalyst is capable of producing arenot particularly limited. It is particularly preferred that the catalystis capable of producing polyethylene and/or polypropylene.

The catalyst component or catalyst system of the present invention areused in the method of the present invention to produce polyolefinresins. It is especially preferred that the method of the presentinvention is a method of producing a polyethylene or a polypropylene.These polyolefins can be monomodal or multimodal.

The conditions employed for polymerisation in the method of the presentinvention are not particularly limited, provided they are sufficient toeffectively polymerise the particular monomeric olefin used as astarting material. When the monomer to be polymerised in the presentmethod is ethylene, the preferred polymerisation conditions are from70-110° C., more preferably from 70-90° C. (e.g. around 80° C.) using ahydrocarbon solvent such as isobutane or hexane. Preferablypolymerisation takes place in the presence of hydrogen and an alkeneco-monomer such as 1-butene or 1-hexene.

The polymerisation process in which the catalyst systems of the presentinvention can be used is not particularly limited. Preferably thecatalysts are employed in a process for polymerising ethylene. Morepreferably the process is a process for producing a polyethylene with abimodal or multimodal molecular weight distribution. Such processes mayemploy a dual site catalyst to achieve bimodality and one or both of thecatalytic sites may be provided by metallocene catalysts as described inthe present invention.

The invention will now be described in further detail by way of exampleonly, with reference to the following non-limiting specific embodiments.

EXAMPLES

Catalyst Preparation

One catalyst component of the present invention, (Me₂Si)(2-MeTHI)₂ZrCl₂(catalyst 1), was prepared in accordance with the method of W. Spalek;A. Antberg, J. Rohrmann, A. Winter, B. Bachmann, P. Kiprof, J. Behm, andW. A. Hermann, Angew. Chem. Int. Eng. Ed. 1992, 31, 1347. A furthercatalyst component of the present invention, (Et)(2-MeTHI)₂ZrCl₂(catalyst 2), was prepared in accordance with the method of H. H.Brintzinger, Journal of Organometallic Chemistry, 1982, 232, 233. Forcomparative purposes two similar catalysts, (Me₂Si)(THI)₂ZrCl₂ and(Et)(THI)₂ZrCl₂ (catalysts 3 and 4 respectively) in which both THIligands were unsubstituted, were prepared. Catalyst 4 was preparedaccording to F. R. W. P. Wild, M. Wasiucuinek, G. Huttner, and H. H.Brintzinger, Journal of Organometallic Chemistry, 1985, 288, 63.

The support used was silica having a total pore volume of 4.22 ml/g anda surface area of 322 m²/g. This silica is further prepared by dryingunder a high vacuum on a schlenk line for three hours to removephysically absorbed water. 5 g of this silica were suspended in a roundbottom flask equipped with a magnetic stirrer, a nitrogen inlet and adropping funnel.

To produce activated catalyst, amounts of approximately 0.3 g ofcatalysts 14 were each reacted with 25 ml of methylalumoxane (MAO 30 wt.% in toluene), at a temperature of 25° C. for 10 minutes to givesolutions of the corresponding metallocene cations and the anionicmethylalumoxane oligomer.

Then the resulting solutions comprising the metallocene cations and theanionic methylalumoxane oligomer were added to the support under anitrogen atmosphere via the dropping funnel, which was immediatelyreplaced with a reflux condenser. The mixtures were each heated to 110°C. for 90 minutes. The reaction mixtures were then cooled to roomtemperature, filtered under nitrogen and washed with toluene.

The catalyst systems obtained were then washed with pentane and driedunder a mild vacuum.

The catalyst systems of the present invention comprising catalystcomponents 1 and 2, and the comparative catalyst systems comprisingcatalyst components 3 and 4, were used to polymerise ethylene. In eachpolymerisation reaction, the ethylene was polymerised in a 4 l benchreactor at 80° C. An isobutane solvent (2 l) was used comprising 6% wt.ethylene. A 1 hr residence time was used. The molecular weight (Mw) ofthe polymer products produced as well as their HLMI values are shownbelow in Table 1. TABLE 1 Unsubstituted Substituted (invention)(comparison) Catalyst Catalyst Catalyst Catalyst Cat. & bridge 1 (Si) 2(Et) 3 (Si) 4 (Et) M_(w)/kDa 399 360 329 326 HLMI 0.15 0.22 0.27 0.22(g/10 mins)

Comparing the properties of the polyethylene products produced by thethird generation catalysts (substituted catalysts of the presentinvention) with the closest second generation catalysts (unsubstituted),it is clear that the catalysts of the present invention give a muchhigher molecular weight product than the comparative catalysts whilstdisplaying a similar or reduced HLMI. This is particularly demonstratedby the M_(w) and HLMI values for catalyst 1 which are 399 k and 0.15respectively, the highest and lowest values for the tested polymers. Itis preferable that the molecular weight is as high as possible tobenefit the mechanical properties of the polymer produced.

The HLMI measured in the above Examples is the high load melt index andis measured according to the procedures of ASTM D 1238 using a load of21.6 kg at a temperature of 190° C.

1-20. (Cancelled)
 21. A catalyst component for producing a polyolefin,which catalyst component comprises a metallocene catalyst having astructure defined by the formula:(THI)₂R″MQ_(p)  (1) wherein each THI is a tetrahydroindenyl derivativewhich may be substituted or unsubstituted provided that at least one ofthe tetrahydroindenyl derivatives is monosubstituted at the 2-positionor polysubstituted with substituents at the 2- and the 4-position withthe substituent at the 4-position having a bulk which is greater thanthe substituent at the 2-position; R″ is a 1,1′ structural bridgeextending between the two THI groups to impart stereorigidity theretoand is selected from a group consisting of a substituted orunsubstituted ethylenyl group or a dialkylsilyl group, provided thatwhere the at least one tetrahydroindenyl group is substituted at the 2-and the 4-position the bridge R″ is a substituted or unsubstitutedethylenyl group; M is a metal from Group IIIB, IVB, VB or VIB; Q is ahydrocarbyl group having from 1-20 carbon atoms, or a halogen; and p isthe valence of M minus
 2. 22. A catalyst component according to claim 21which comprises a metallocene catalyst of formula (1) in which both ofthe THI derivatives are substituted THI derivatives.
 23. A catalystcomponent according to claim 21 which comprises a metallocene catalystof formula (1) in which said at least one THI derivative hassubstituents at both of the 2-position and the 4-position.
 24. Acatalyst component according to claim 23 which comprises a metallocenecatalyst of formula (1) in which both of the THI derivatives comprisesubstituents at both the 2-position and the 4-position.
 25. A catalystcomponent according to claim 24 wherein both of the THI derivatives havethe same pattern of substitution.
 26. A catalyst component according toclaim 24, wherein the substituents on the THI derivatives areindependently selected from Ph, Bz, Naph, Ind, BzInd, Me, Et, n-Pr,I—Pr, n-Bu, t-Bu, and Me₃Si, subject to the provision that substituentsat the 4-position have a greater bulk than substituents at the2-position.
 27. A catalyst component according to claim 26, wherein thesubstituents comprise methyl groups at the 2-position and phenyl groups,naphthyl groups, or benzindenyl groups at the 4-position.
 28. A catalystcomponent according to claim 21, wherein M is Ti, Zr, Hf, or V.
 29. Acatalyst component according to claim 28, wherein Q is Cl.
 30. Acatalyst component according to claim 29, wherein p is
 2. 31. A catalystcomponent according to claim 30, wherein R″ comprises an unsubstitutedethylenyl group.
 32. A catalyst component according to claim 21, whereinthe metallocene catalyst is immobilized on a solid support.
 33. Acatalyst system comprising a catalyst component as defined in claim 21,and further comprising an aluminum- or boron-containing co-catalystcapable of activating the catalyst component.
 34. A process forproducing a polyolefin which comprises: a. providing a catalyst systemfor producing a polyolefin which catalyst system comprises a metallocenecatalyst component having a structure defined by the formula:(THI)₂R″MQ_(p)  (1) wherein each THI is a tetrahydroindenyl derivativewhich may be substituted or unsubstituted provided that at least one ofthe tetrahydroindenyl derivatives is monosubstituted at the 2-positionor di-substituted at the 2- and the 4-position with the substituent atthe 4-position having a bulk which is greater than the substituent atthe 2-position; R″ is a 1,1′ structural bridge extending between the twoTHI groups to impart stereorigidity thereto and is selected from a groupconsisting of a substituted or unsubstituted ethylene group or adialkylsilyl group, provided that where the at least onetetrahydroindenyl group is substituted at the 2- and the 4-position thebridge R″ is a substituted or unsubstituted ethylenyl group; M is ametal from Group IIIB, IVB, VB or VIB; Q is a hydrocarbyl group havingfrom 1-20 carbon atoms, or a halogen; and p is the valence of M minus 2and an aluminum- or boron-containing co-catalyst capable of activatingthe catalyst component; b. contacting said catalyst system with anolefin monomer in a polymerization reaction zone under polymerizationconditions to form a polyolefin product; and c. withdrawing saidpolyolefin product from said polymerization reaction zone.
 35. Theprocess of claim 34 wherein said metallocene catalyst is immobilized ona solid support.
 36. A process according to claim 34, wherein the olefinmonomer is ethylene or propylene and said polyolefin product ispolyethylene or polypropylene.
 37. A process according to claim 36wherein said catalyst system comprises a second metallocene catalystcomponent as defined by formula (1) to provide a dual site catalystsystem and wherein said polyolefin product comprises a multimodalpolyolefin.
 38. The process of claim 37 wherein said olefin monomer isethylene and said polyolefin product is multimodal polyethylene.
 39. Theprocess of claim 34 wherein said catalyst system comprises themetallocene catalyst component of formula (1) in which both of the THIderivatives comprise substituents at both the 2-position and the4-position.
 40. The process of claim 37 wherein both of the THIderivatives of said catalyst component have the same pattern ofsubstitution.